1. Field of the Invention
The present invention relates to a manhole and, more specifically, to a manhole cover mounting structure that can be conveniently adjusted to lift the elevation of the inner frame thereof when sank under the load, keeping the cover plate in flush with the road surface.
2. Description of the Prior art
In underground piping construction, a manhole or handhold box is provided in the road surface through which a worker or the hand can enter the water conduit to install a piping system or make a repair work. FIGS. 1 and 2 show a manhole box mounting structure according to the prior art. The manhole box mounting structure comprises a manhole box 1, a frame 11 on the manhole box and embedded with the manhole box 1 in reinforcing concrete RC, and a cover plate 12 covered in the frame 11. This structure of manhole cover mounting structure has drawbacks as follows:
1. After the manhole box 1 embedded in the ground, the frame 11 is not maintained in flush with the road surface, and pebbles 13 are used to support the frame 11 above the manhole box 1 and to keep the frame 11 in flush with the road surface, and then reinforcing concrete RC is applied to fix the frame 11 and the manhole box 1to the ground. Because the color of applied reinforcing concrete RC does not fit the color of the asphalt AC of the road surface, it destroys the sense of beauty of the road surface.
2. If the frame 11 sinks under the load of vehicles passed, reinforcing concrete RC must be removed so that the elevation of the frame 11 can be adjusted to hold the cover plate 12 in flush with the road surface. This elevation adjusting procedure is complicated.
There are known manhole cover mounting structures in which the cover plate can be adjusted vertically relative to the frame and the manhole box. However, because the elevation of the frame is not adjustable, the adjustment of the cover plate is limited to a narrow range.
The present invention has been accomplished to provide a manhole cover mounting structure, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide a manhole cover mounting structure, which can conveniently be adjusted to the desired elevation, keeping the cover plate in flush with the road surface. It is another object of the present invention to provide a manhole cover mounting structure, which fits manholes of any of a variety of shapes. It is still another object of the present invention to provide a manhole cover mounting structure, which stable and durable in use. It is still another object of the present invention to provide a manhole cover mounting structure, which can be adjusted at a single side or single point subject to the sloping condition of the road surface. To achieve these and other objects of the present invention, the manhole cover mounting structure of the present invention comprises a manhole box, the manhole box having a plurality of screw nuts fixedly provided at a top side thereof; an outer frame fixedly fastened to screw nuts of the manhole box by screw bolts; an inner frame mounted in said outer frame; and a cover plate covered on the inner frame in flush with the topmost edge of the inner frame; wherein: the outer frame comprises a plurality of locating blocks disposed around the periphery thereof, the locating blocks each comprising a top-open hollow body and an upright guide rod disposed in the hollow body, the upright guide rod having an axially upwardly extended screw hole; the inner frame comprises a plurality of lugs spaced around the periphery thereof corresponding to the locating blocks of the outer frame, the lugs each having a through hole, a plurality of female screws respectively fixedly fastened to the lugs at a bottom side and axially aligned with the through hole of each of the lugs, and a plurality of screw rods respectively threaded into the female screws, the screw rods each having an axially extended, stepped through hole formed of an upper polygonal hole and a lower coupling hole, which receives the upright guide rod of each of the locating blocks of the outer frame; a plurality of through bolts are respectively inserted into the upper polygonal hole and lower coupling hole of each screw rod at each of the lugs of the inner frame and threaded into the screw hole of the upright screw rod of each of the locating blocks of the outer frame to secure the inner frame to the outer frame.